Precise limiting of fast rise-time narrow (e.g., less than 100 nano-Second) pulses of relatively low amplitude (e.g., &lt;1 volt) presents a technical challenge. It is especially true when the available hardware is limited by cost, board area or other construction considerations. The conventional limiters using diode, or Zener diode, junction or saturation characteristics of a transistor either do not work at all in the case of very narrow and small amplitude pulses (e.g., 100 n-Second, 1 volt) or do not guarantee acceptable performance. Such pulses are commonly encountered, for example, in video signal processing circuits.
As an example, it is common practice to apply peaking to luminance signals for improving the apparent sharpness of image edges. Certain types of peaking circuits, however, create overshoots which are acceptable at most video signal levels but which may exceed 100 IRE levels for signals at or near peak white. Exceeding the peak white levels may, in turn, lead to undesired saturation or "blooming" effects and so it would be desirable to limit or "clip" overshoots exceeding peak white levels. A particular problem in limiting pulses of short duration and relatively low amplitude is delayed response. Other applications in which fast pulse limiting action would be desirable include noise limiters in communications equipment, input signal conditioners in analog to digital converters and so forth.